Process and flux for solder bonding on coated metal surfaces



Patented May 30, 1939 UNITED STATES PATENT OFFICE PROCESS AND FLUX FOR SOLDER BONDING N COATED METAL SURFACES 1 Norman J. Beno, Chicago, 111., assignor to Continental Can Company, Inc., New York, N. Y., a corporation of New York No Drawing. Application February 18, 1935, Serial hi0. 1,145

3 Claims. (0]. 113-112 a In many industries it is essential to bond or ;to prevent crystallization. Any salt which crysjoin metal surfaces. This bonding is normally tallizes is easily re-dissolved by warming the flux. accomplished by heating a bonding material in It is possible to dilute the highly concentrated and the presence of a fluxing agent. The bonding strong fiux thus produced with water or alcohol material includes the alloys known as solders. to a desired extent. T

5 The flux is employed for preparing the metal sur- The flux solution is milky in appearance and faces and to protect them and the solder during this milkiness becomes more pronounced as the the uniting. flux is diluted. If desired, 2 to 3' percent of con- Certain dimculties are encountered in bonding centrated hydrochloric acid may be added, prefprotected metal surfaces such' as zinc plate, comerably to the water when the salts are dissolved, m prising a base of steel having a thin electroand this will in most cases prevent the formadeposited coating of zinc thereon. The zinc must tion of the milkiness or any milky precipitate. be removed for a proper bonding by the solder The existence of the said precipitate, however, upon the surface of the base plate itself. Heredoes not appear to interfere with the proper optofore it has been customary to remove the plateration of the flux. 15 ing by a separate'mechanical or chemical opera- In operation, the flux is applied to the coated tion and thereafter to prepare the treated plate metal and an exchange then occurs between the for the bonding. tin in the flux and the zinc of the coating, re-

. According to the present invention, it is pfosulting in the production of zinc chloride in the .p0sed to employ a treating material which in- *rflux liquid and a deposit of tin upon the plate.

' corporates in itself means for removing the plat- The action is very rapid. The application of the ing and also for establishing a flux during the solder alloy and heating appears to cause a blend'- bonding operation proper. ing of the solder alloy with the deposited tin, so

The invention is applicable to metal surfaces that a very firm union results, the metal and in general which have protective coatings theresolder being protected by the flux.

' and Comprises the utilization as a flux u Asimilar action is attainable with the stannous ing the bonding operation of a composition inchloride itself, but this does not appear so satisclu n a metal W h is l otronegative with re% factory as the flux composition set out above. $13801; to the metal of t p a and thereby This composition can also be employed with x h 'ne s wi h t e am to compl sh he re metal surfaces of iron, steel and the like base m va o t e coa metal- In the preferred metals customarily employed when coated with f rm, th pr du t r su t r t exchange i cadmium, tin, aluminum and similar metals para metal salt which is operative as a flux during ticularly when deposited electrolytically, in conthe bonding operation. junction with the provision of a salt of a metal As p fi example o p a of h s invenwhich is electronegative with respect to the metal tion for the purpose of solder-bonding sheets of f th coating, such as stannous chloride, copper steel electroplated with zinc, which is partlcuhloride, etc. larly advantageous in the formation of metal con- Having t described t i ti h t 1 tainers from such sheets, the following comp s claim as new and desire to secure by Letters Pat- 40 tion is employed: cut, is:

Pounds Ounces 1. A surface treatment and fiuxing composi- S a chloride Crystals tion for solder bonding on steelsurfaces having (SnCl22H2O) 9 protective coatings of zinc and like metals there- Zinc Chloride (Z Ch) 2 on, comprising approximately 9%; pounds of Ammonium Chloride (NH4CD 0 stannous chloride, approximately 3 pounds of 45 Waterzinc chloride and approximately 3 percent of am- A part of the water is heated, thei stannous .monium chloride 'dissolvedin water to provide an chlorideintroduced, and the heat maintained unaqueous Solution havmg a ensity of approxitilthe salt .goes'into solution. The other ingredimately degrees a room temperatureents are dissolved in the remaining water in the I A Surface treatment a d fiuxing composi- 50 cold. The two solutions are then mixed. The "tion for Solder bondmg 011 Steel Surfaces having product is about 1 gallon of flux 61 about '10 protective coatings of zinc and like metals theredegrees B on, comprising approximately 9%, pounds of At this concentration, the flux should be kept stannous chloride, approximately 3 pounds of at a temperature of about degrees F. or above zinc chloride and approximately 3 percent of 5 ammonium chloride dissolved in water to provide an aqueous solution having a density of approximately '70 degrees B. at room temperature, and also containing approximately 2 to 3 percent of concentrated hydrochloric acid.

3. The method of establishing a solder bond at steel surfaces having protective coatings of zinc and like metal thereon, which comprises locally applying a flux comprising an aqueous solution having a density of approximately 70 degrees B. at room temperature and containing approximately 9 pounds of stannous chloride, approximately 3 pounds of zinc chloride, and approximately 3 percent of ammonium chloride, the metal being heated to about 80 degrees R, whereby the zinc or like metal of the coating is removed and converted to the chloride thereof and the tin of the stannous chloride is deposited in metallic 5 residual chlorides as a flux for the soldering 10 N O J. EH30.

operation. 

